Evolution, 55(7), 2001, pp. 1408±1418 RAPID EVOLUTION IN THE NEBRIA GREGARIA GROUP (COLEOPTERA: CARABIDAE) AND THE PALEOGEOGRAPHY OF THE QUEEN CHARLOTTE ISLANDS T. E. CLARKE,1,2 D. B. LEVIN,1,3 D. H. KAVANAUGH,4,5 AND T. E. REIMCHEN1,6,7 1Department of Biology, University of Victoria, P.O. Box 3020, Victoria, British Columbia, V8W 3N5, Canada 2E-mail: [email protected] 3E-mail: [email protected] 4Department of Entomology, California Academy of Sciences, Golden Gate Park, San Francisco, California 94118 5E-mail: [email protected] 6E-mail: [email protected] Abstract. Morphological differentiation in the ground beetles of the Nebria gregaria group, found on the Queen Charlotte Islands, has been used as support for the glacial refugium proposed for the northwest coast of North America. Two members of this species group, N. charlottae and N. louiseae, are restricted to cobble beaches in this archipelago. A third, N. haida, is found only in alpine regions of the archipelago and the adjacent mainland. The remaining two species of the gregaria group, N. lituyae and N. gregaria, show highly restricted distributions in the mountains of the Alaska panhandle and on the beaches of the Aleutian Islands, respectively. To determine the relationships of the ®ve species, we conducted phylogenetic analyses on nucleotide sequence data obtained from ®ve regions of the mito- chondrial DNA. In total, 1835 bp were analyzed. The results suggest that one species, N. lituyae, does not belong in the gregaria group, and that only seven mutations separated the two most divergent of the four remaining species. We also conducted random ampli®ed polymorphic DNA ®ngerprinting analyses on genomic DNA extracted from the ®ve species. Analyses of genetic diversity revealed a lack of molecular differentiation among the Queen Charlotte species, suggesting that these populations may be postglacial in origin and that together N. gregaria, N. charlottae, N. louiseae, and N. haida might represent local variations of a single species. These results are consistent with conclusions derived for the morphological and genetical differentiation among Gasterosteus populations in the ar- chipelago. Key words. Carabidae, glacial refugium, mitochondrial DNA, molecular evolution, phylogenetic analysis, Queen Charlotte Islands, random ampli®ed polymorphic DNA. Received August 29, 2000. Accepted March 25, 2001. The glacial cycles of the late Pleistocene have de®ned the during periods of global warming (Fjeldsa and Lovett 1997; current biogeography of North America, affecting both the Roy 1997; Smith et al. 1997). The physical refugia generated composition and distribution of the animal and plant species. by the ice sheets along the coast of northern North America The regular glacial advances and retreats have resulted in the may have played a similar role in promoting speciation by movement of species across vast distances and the reorga- maintaining populations in isolation from each other for pe- nization of many ecological communities in their wake. Gla- riods of several tens of thousands of years. cial advances have occurred with a period of approximately On the northwest coast of North America, glacial refugia every 100,000 years with the most recent (Wisconsin) ice may have existed on Kodiak Island (Karlstrom and Ball age beginning approximately 70,000 years ago, reaching a 1969), the Alaskan panhandle (Kavanaugh 1988), and the maximum extent during the Frasier glaciation between Queen Charlotte Islands (Foster 1965), with the evidence 25,000 and 15,000 years ago. (Liu 1992). At the height of based primarily on taxa that are either endemic to the refugia the Frasier glaciation ice sheets occupied much of the north- or display disjunct distributions. For the Queen Charlotte ern half of the continent, leaving only a scattering of localities Islands, the largest of the hypothesized western refugia, the along the coast uncovered (Blaise et al. 1990). These ice- assemblage of endemic, dispersing, and disjunct taxa has free refugia existing along the edge of the ice sheets are included mammals (Foster 1965), birds (Cowan 1989), in- known for their role in maintaining species diversity through sects (Hamilton 1982; Ferguson 1987; Kavanaugh 1989), the glaciations by sheltering species and subspecies that plants (Scho®eld 1989; Taylor 1989), and lichens (Brodo would otherwise have risked extirpation. Refugia have also 1995). Although the glacial geology of the islands has sug- contributed to the biogeography of North America by allow- gested no refugia other than possible coastal beaches and ing these species to rapidly colonize adjacent land in the wake mountaintop nunataks (Brown and Nasmith 1962), recent of the glacial retreat (Pielou 1991). Whether coastal refugia data suggest a possible refugial source area in the now sub- have contributed to speciation, however, is still a topic of merged continental shelf separating the archipelago from the debate. In the South American and African tropics, the pe- continent, as lowered sea levels may have exposed wide riodic ¯uctuations in global temperature that have charac- stretches of this terrain during the glacial period (Barrie et terized the late Pleistocene have promoted speciation through al. 1993; Josenhans et al. 1995). the creation of ecological refugiaÐisolating populations in One criterion used in evaluating evidence for glacial re- fragmented forest and grassland ecosystems (Haffer 1977; fugia is the extent of morphological differentiation or en- Colinvaux 1998; Danin 1999) or on mountains and highlands demism in local biota. Similarity between the source popu- lations on the continent and those on the adjacent islands 7 Corresponding author. suggests recent, presumably postglacial colonization, where- 1408 q 2001 The Society for the Study of Evolution. All rights reserved. MOLECULAR EVOLUTION IN NEBRIA 1409 as marked dissimilarity suggests long-term separation. Yet the latter possibility pivots on the broad assumption that mor- phological change accrues slowly within isolated populations and that only the most minor of differences between popu- lations were likely to have occurred in postglacial time (McCabe and Cowan 1945; Foster 1965). Under a more rig- orous evaluation, however, the basis for this assumption would appear to be unfounded. Numerous examples of rapid postglacial morphological change have been documented, in- cluding the repeated evolution of benthic and limnetic morphs of ®sh (McPhail 1992) and size differences in insular rodent fauna (Angerbjorn 1986). On the Queen Charlotte Ar- chipelago, studies on threespine stickleback demonstrate that the extreme population variation in body form and armor is an adaptive response to differences in the predator regimes among localities (Moodie and Reimchen 1976; Reimchen et al. 1985; Reimchen 1994), although there is evidence for deep phylogenetic branching among populations (O'Reilly et al. 1993; Deagle et al. 1996). Similarly, a molecular study of west coast black bears demonstrated that the morphologically FIG. 1. Phylogeny of the Nebria gregaria infragroup (Kavanaugh distinct Queen Charlotte Islands subspecies (Ursus ameri- 1989). canus carlottae) is very similar genetically to the coastal mainland bear population, indicating that the island and coastal subspecies have diverged very recently and that the with habitat, grouping the alpine-dwelling species N. lituyae morphological differences are likely an adaptation to differ- and N. haida into one lineage and the beach-dwelling species ences in their respective habitats (Byun et al. 1997, 1999). N. gregaria, N. charlottae, and N. louiseae into a second. The evidence that morphology can change rapidly, and has Later periods of refugial isolation acted to produce the ®ve done so repeatedly through the postglacial period, necessi- species, with the most recent division between N. gregaria tates a reexamination of the endemic Queen Charlotte Islands and N. louiseae believed to have occurred as a product of the and western coastal taxa that have been used to support ev- Fraser glaciation (Fig. 1; Kavanaugh 1979a, 1989, 1992). idence for glacial refugia during the Fraser glaciation. Evidence for morphological stasis and the extended periods The ground beetles of the Nebria gregaria group, distrib- of time required for reproductive isolation within the pre- uted intermittently along the northwestern coast of North dacious ground beetles are based on data derived from pa- America from the Queen Charlotte Islands to the Aleutians, leoentomological studies of insect fossils from the high-arctic are considered to be a taxon for which the repeated isolation tundra, which show highly conserved morphology (Matthews of populations in glacial refugia has played an important role 1980; Ashworth 1996). As such, the marginal morphological in the promotion of speciation (Kavanaugh 1992). Composed differentiation in the gregaria group is thought to represent of ®ve morphologically similar species, the members of the multiple phases of speciation and stasis, beginning in the Nebria gregaria group display a remarkable degree of en- Early or Middle Pleistocene (Kavanaugh 1989). Yet, in view demism to locations associated with hypothesized glacial re- of the rapid morphological change observed in other Queen fugia. The three Queen Charlotte Island species consist of N. Charlotte taxa, we test here whether the diversi®cation of the charlottae, which is restricted to cobble beaches on Graham gregaria group is a recent event, either due